I have tried to install NetBSD 7.1 and 7.99.67 on a Thinkpad x240. With both versions I had massivly installtion problems but i reached the end of the installation program. But when I reboot I get always the media select menu, when I choose the harddisk it returned instantly back to the menu.
I also played with different BIOS setups but no luck the get a hint what is broken in NetBSD.

I have updated the UEFI-BIOS to the latest version. UEFI Secure Boot is off, no changes.
So I exchanged my old hdd from the x220(x200) to x240 and it runs. For me it looks like another bug in the sysinst installer.